The clinical program aimed at identifying the reaction products of stannous fluoride (SnF2) with enamel was initiated in January, 1975. The program consists of a clinical visit every six months, in which the patients receive instructions in oral health care, a topical application of a 0.4% SnF2 gel, and a clinical charting of the decayed, missing and filled teeth. These patients then receive a home supply of toothpaste containing SnF2 for daily use and 0.4% SnF2 gel for weekly use. The efficacy of the application of a 0.4% SnF2 in reducing dental caries over a two and a half year period will be computed. One of the maxillary anterior teeth is biopsied for F minus concentration. Primary teeth near exfoliation receive a topical application of 10% SnF2 solution. These teeth are then biopsied and analyzed for tin and F content. Neither the acid etch biopsies performed in vivo nor the in vitro studies of exfoliated teeth have revealed the Sn3F3PO4 reaction. The tin measurable in some in vitro biopsy samples gave a Sn/P of only 0.7, which is far below the Sn/P ratio in Sn3F3PO4. Studies will continue on the reaction products formed from treatment with SnF2 solutions. The solubility study of the Sn3F3PO4 compound faces some problems with reprecipitation of Sn and P from the solution. Additional in-depth experiments aimed at deriving the solubility product (Ksp) are necessary to obtain meaningful information about the solubility of Sn3F3PO4 in acids. The deterioration of 10% stannous fluoride solutions in glass and polyethylene containers was also studied. This study clarified the deterioration of aqueous solutions of SnF2 with time and showed that the solution may be used clinically over several days without significant loss of fluoride and stannous ion activity. BIBLIOGRAPHIC REFERENCES: Nordquist, W.D., Krutchkoff, D.J., and Wei, S. H. Y.; "Effect of Prior Acid Etch on Rate of Sn3F3PO4 Formation Subsequent to Topical Application of SnF2." J. Dent Res., 54: 1154-1160, 1975. Wei, S.H.Y., Tang, T.E., and Wefel, J.S., "The Deterioration of SnF2 Solutions in Glass and Polyethylene Containers", Internation Association for Dental Research, annual meeting. March 1976, Miami Beach, Fla. abstract.